Apparatus for separating plastic chips

ABSTRACT

A first and second electrostatic sorting sections are arranged below a tribo-electrifying device in this order in a vertical direction to form a sorting electrostatic field between a drum electrode and an opposing electrode. Plastic pieces separated from the other plastic pieces by the sorting electrostatic field in the first electrostatic separating section are introduced into a sorting electrostatic field in the second electrostatic separating section for second separation, thereby increasing the separation purity and recovery rate of plastic pieces.

TECHNICAL FIELD

The present invention relates to a plastic sorting apparatus for sortingcrushed plastic pieces composed of plural types of plastics, accordingto their types.

BACKGROUND ART

A conventional plastic sorting apparatus comprises two electrode platesarranged parallel with each other in a vertical direction so as to forma space of a predetermined size therebetween, the electrode plateshaving a high-voltage power supply connected thereto to form aseparating electrostatic field therebetween, wherein plastic pieces areloaded into the separating electrostatic field from above, and theelectrostatic force of the separating electrostatic field is used tovary the falling trajectories of the plastic pieces correspondingly tothe charges of the plastic pieces, thereby separating the plastic piecesfrom one another according to their type.

However, to improve the separation precision of the conventionalapparatuses, it is necessary to use long electrode plates to increasethe time required for the plastic pieces to pass through the separatingelectrostatic field, which disadvantageously requires the size of theapparatuses to be increased. Further, the plastic pieces may adhere tothe electrodes, resulting in degraded separation performance, to hindercontinuous processing.

Thus, the inventors have proposed the plastic sorting apparatus shown inFIG. 9 as a technique for sorting out crushed plastic pieces. Thisplastic sorting apparatus is composed of a hopper 100 into which plasticpieces a and b including two or more types mixed together are loaded, atribo-electrifying device 101 arranged below the hopper 100 to stir theplastic pieces a and b of different types to contact them with eachother, thereby electrifying the plastic pieces a and b to the respectivepolarities and electrification amounts according to their type, and anelectrostatic separating device 105 that separates the plastic pieces aand b from each other by applying a high voltage from a high-voltagepower supply 104 to a drum electrode 102 and an opposing electrode 103both arranged below the tribo-electrifying device 101, to form a sortingelectrostatic field Ea.

In this plastic sorting apparatus, the tribo-electrifying device 101frictionally contacts the plastic pieces a and b of different types witheach other to tribo-electrify them to the respective polarities andelectrification amounts corresponding to an electrification array. Then,when the plastic pieces a and b are fed-onto the drum electrode 102,image force is applied to the plastic pieces a and b, which are thenattracted to a surface of the drum electrode 102 and carried to thesorting electrostatic field Ea. Then, in the sorting electrostatic fieldEa, electrostatic force and centrifugal force are applied to the plasticpieces a and b, so that the forces acting on the plastic pieces b havingthe same polarity (−) as that of the drum electrode 102 are such thatimage force<(electrostatic force+centrifugal force). As a result, theplastic pieces b fall so as to follow falling trajectories extendingfrom a surface of the metal drum electrode 102 to the opposing electrode103 and are thus collected in a separation container 106. On thecontrary, the forces acting on the plastic pieces a having a polarityopposite to that (−) of the drum electrode 102 are such that (imageforce+electrostatic force)>centrifugal force, so that the plastic piecesa remain attracted to the drum electrode 102 or fall so as to followfalling trajectories approaching the drum electrode 102 and are thencollected in a separation container 107.

Methacryl resin [acrylic resin] (hereinafter referred to as “PMMA”),polyethylene resin (hereinafter referred to as “PE”), polypropyleneresin (hereinafter referred to as “PP”), and vinyl chloride resin(hereinafter referred to as “PVC”) occupy about 80% of all the plasticsconsumed as material for plastic products. Further, polyethyleneterephthalate resin (hereinafter referred to as “PET”) used for PETbottles is separately sorted out and recovered. To use these resins asrecycle material for material recycling, they must be precisely (99% ormore) sorted out according to their type.

Further, it is contemplated that in order to achieve a high purity and ahigh recovery rate with the electrostatic separating device 105 of theabove described plastic sorting apparatus, a separator 108 arranged atthe boundary between the separation containers 106 and 107 may pivot indirections A and B to adjust a separation position so as to improve thepurity.

FIG. 10 shows the relationship between the recovery rate and purityobtained by the inventors through sorting experiments in which the angleof the separator 108 was adjusted. In this figure, the purity and therecovery rate are determined using the following equation:

Recovery rate (%)=weight (g) of plastic pieces of a target typecollected in a predetermined separation container/total weight ofplastic pieces of the target type loaded into an electrostaticseparating device.

Purity (%)=weight (g) of plastic pieces of a predetermined typecollected in a predetermined separation container/weight of all plasticpieces collected in the separation container.

FIG. 10 indicates that it is likely that an increase in purity reducesthe recovery rate, whereas an increase in recovery rate reduces thepurity. Thus, if plastic pieces are to be recovered according to theirmaterial, the rate at which plastic pieces are recovered becomesinsufficient to make the separating operation less efficient even if theplastic pieces have an attainable purity of 99% or higher.

Further, with a lower voltage applied to the drum electrode 102 andopposing electrode 103, the field intensity of the sorting-electrostaticfield Ea decreases to reduce changes of the falling trajectories ofplastic pieces a and b, thereby reducing the precision (purity andrecovery rate) with which the plastic pieces a and b are separated fromeach other. Thus, to increase the separation precision for the plasticpieces a and b, a high-voltage electrode 6 with a much higher voltagemust be used to form a sorting electrostatic field Ea of an increasedfield intensity. In this case, however, a very high voltage must beapplied to the metal drum electrode 102 and opposing electrode 103, andall members of the electrostatic separating device 105 must thus havehigh-voltage-resistant and highly-insulated structures, therebysubstantially increasing facility costs. Consequently, it is difficultto apply a voltage exceeding a predetermined value.

Furthermore, when plastic pieces PMMA, PE, PP, and PVC aretrobo-electrified using the tribo-electrifying device 101, they areelectrified to their respective polarities and electrification amountsin accordance with the electrification array of (+ side) PMMA-PE-PP-PVC(− side). For example, if PE and PP, which are closely ordered in theelectrification array, are contacted with each other fortribo-electrification, the PE is electrified to (+), while the PP iselectrified to (−), with a small difference in electrification amounttherebetween. Accordingly, if different types of plastic pieces aremixed together which are closely ordered in the electrification arrayand have only a small difference in electrification amount therebetween,then a problem with the above described conventional plastic sortingapparatus is that the plastic pieces cannot be sorted out with a highpurity of 99% or higher and a high recovery rate.

It is an object of the present invention to provide a plastic sortingapparatus that can sort out plastic pieces according to their type witha high purity and a high recovery rate.

SUMMARY OF THE INVENTION

The present invention provides a plastic sorting apparatus comprising atribo-electrifying section that causes plural types of plastic pieces tofrictionally contact with one another for electrification, and anupper-stage electrostatic separating section, a lower-stageelectrostatic separating section and a recovery section which are alllocated-below the tribo-electrifying section downwardly in this order,characterized in that the upper and lower-stage electrostatic separatingsections each comprises a metallic rotationally-movable electrode havinga top portion to which plastic pieces-are fed, an opposing, electrodelocated to oppose a downwardly-moving portion of the rotationallymovable electrode, and a high-voltage power supply for applying a highvoltage to the rotationally movable electrode and opposing electrode toform a separating electrostatic field therebetween, in that a connectionsection is provided for feeding the rotationally movable electrode ofthe lower-stage electrostatic separating section with plastic piecesseparated toward the rotationally movable electrode in the upper-stageelectrostatic separating section, and in that polarities applied by thehigh-voltage power supply respectively to the rotationally movableelectrode and opposing electrode in the upper-stage electrostaticseparating section are opposite to polarities applied by thehigh-voltage power supply to the rotationally movable electrode andopposing electrode in the lower-stage electrostatic separating section.

According to this construction, the upper- and lower-stage electrostaticseparating sections, arranged in the vertical direction toelectrostatically separate and sort out electrified plastic piecesaccording to their polarity and electrification amount, are locatedbelow the tribo-electrifying device which stirs and tribo-electrifiesthe plastic pieces, so that plastic pieces attracted to the rotationallymovable electrode in the upper-stage electrostatic separating section orfollowing falling trajectories approaching the rotationally movableelectrode, are fed to the second electrostatic separating section viathe connection section. Most of these plastic pieces are of a targettype and have charges of a polarity opposite to that of the rotationallymovable electrode of the first electrostatic separating section. In thesecond electrostatic separating section, the plastic pieces of thetarget type are caused to repel the rotationally movable electrode andrecovered, while a small amount of plastic pieces of different types arecaused to be attracted to the rotationally movable electrode or tofollow the falling trajectories approaching the rotationally movableelectrode for separation. Consequently, the plastic pieces of the targettype can be sorted out at a high purity and a high recovery rate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an entire plastic sorting apparatusaccording to a first embodiment of the present invention;

FIG. 2 is a graph showing a mixture ratio of plastic pieces of differenttypes vs. a purity of plastic pieces separated toward an opposingelectrode;

FIG. 3 is a schematic diagram of an entire plastic sorting apparatusaccording to a second embodiment of the present invention;

FIG. 4 is a schematic diagram of an entire plastic sorting apparatusaccording to a third embodiment of the present invention;

FIG. 5 is a schematic diagram of an entire plastic sorting apparatusaccording to a fourth embodiment of the present invention;

FIG. 6 is a schematic diagram of an entire plastic sorting apparatusaccording to a fifth embodiment of the present invention;

FIG. 7 is a schematic diagram of an entire plastic sorting apparatusaccording to a sixth embodiment of the present invention;

FIG. 8 is a schematic diagram showing a variation of an electrostaticseparating section;

FIG. 9 is a schematic diagram of an entire conventional plastic sortingapparatus; and

FIG. 10 is a graph showing a relation between an angle of a separator ofthe conventional plastic sorting apparatus and purity/recovery rate ofplastic pieces.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will be described in further detail with referenceto the attached drawings.

First, a first embodiment of a plastic sorting apparatus according tothe present invention will be described with reference to FIGS. 1 and 2.

This plastic sorting apparatus comprises a tribo-electrifying device 1that stirs at least two different types (materials) of plastic pieces(for example, plastic crushed waste to be sorted out) a and b mixedtogether to frictionally contact the different types of plastic pieces aand b with each other in order to tribo-electrify the plastic pieces torespective polarities and electrification amounts in accordance withtheir order in an electrification array, an upper-stage electrostaticseparating section 10 arranged below an exit 1 a of thetribo-electrifying device 1 to electrostatically separate the pluraltypes of plastic pieces a and b from each other, and a lower-stageelectrostatic separating section 30 arranged below the upper-stageelectrostatic separating section 10 to further electrostaticallyseparate one of the plural types of plastic pieces a and b separated bythe upper-stage electrostatic separating section 10. An upper-stageconnection section (connection section) 20 is provided between theupper-stage electrostatic separating section 10 and the lower-stageelectrostatic separating section 30 to guide the separated plasticpieces. Further, a recovery section 40 is provided below the lower-stageelectrostatic separating section 30.

The upper-stage electrostatic separating section 10 comprises a metalliccylindrical upper-stage drum electrode 11 (rotationally movableelectrode) arranged below the tribo-electrifying device 1 androtationally driven at a predetermined velocity (peripheral velocity) inthe direction of an arrow in the figure (clockwise) around a horizontalshaft, a supply chute 12 of, for example, a vibrating type which feedsan upper end of the upper-stage drum electrode 11 with a fixed amount ofthe plastic pieces a and b supplied by the tribo-electrifying device 1,an upper-stage opposing electrode 13 arranged obliquely above a portionof the upper-stage drum electrode 11 which rotationally moves downward,so as to form a space of a predetermined size between the drum electrodeand the opposing electrode, and an upper-stage scraper 14 slidablycontacting with the portion of the upper-stage drum electrode 11 whichrotationally moves downward, to scrape off the plastic pieces a and btherefrom. Then, for example, a positive electrode (+) of thehigh-voltage power supply 2 is connected to the upper-stage opposingelectrode 13, while a negative electrode (−) thereof is connected to theupper-stage drum electrode 11 via an earth by a feeding brush 2 a.Consequently, an upper-stage separating electrostatic field Ea1 isformed between the upper-stage drum electrode 11 and the upper-stageopposing electrode 13.

Further, the upper-stage connection section 20 has an upper-stageloading chute 21 and an upper-stage recovery conveyor 22 arrangedtherein, the upper-stage loading chute 21 collecting plastic pieces a(including a small number of plastic pieces b) electrified to a (+)polarity and separated from the other plastic pieces toward theupper-stage drum electrode 11, the upper-stage recovery conveyor 22collecting plastic pieces b (including a small number of plastic piecesa) electrified to a (−) polarity and separated from the other plasticpieces toward the upper-stage opposing electrode 13. An upper-stageseparator (separator) 23 is arranged between the upper-stage loadingchute 21 and the upper-stage recovery conveyor 22, and comprises aseparation plate arranged immediately below a peripheral side end of theupper-stage drum electrode 11 and the lower end of which is caused topivot around an axis parallel with the axis of the upper-stage drumelectrode 11 so as to adjust the separation conditions for plasticpieces a separated toward the upper-stage loading chute 21 and plasticpieces b separated toward the upper-stage recovery conveyor 22. Theseparation plate of the upper-stage separator 23 is caused to pivot by amanual rotationally-movable mechanism or actuator (not shown) so as toseparate the plastic pieces a and b from each other with a desiredpurity.

The lower-stage electrostatic separating section 30 comprises a metalliccylindrical lower-stage drum electrode 31 (rotationally movableelectrode) arranged below an exit of the first guide chute 21 androtationally driven at a predetermined velocity (peripheral velocity) inthe direction of an arrow in the figure (counterclockwise) around ahorizontal shaft parallel with the upper-stage drum electrode 11, alower-stage opposing electrode 32 arranged obliquely above a portion ofthe lower-stage drum electrode 31 which rotationally moves downward, soas to form a space of a predetermined size between the drum electrodeand the opposing electrode, and a lower-stage scraper 33 slidablycontacting with the portion of the lower-stage drum electrode 31 whichrotationally moves downward, to scrape off the attracted plastic piecestherefrom. The positive electrode (+) of the high-voltage power supply 2is connected to the lower-stage drum electrode 32 via a feeding brush 2b, while the negative electrode (−) thereof is connected to thelower-stage opposing electrode 32 via an earth. Consequently, alower-stage sorting electrostatic field Ea2 is formed between thelower-stage drum electrode 31 and the lower-stage opposing electrode 32.

Furthermore, the recovery section 40 has a lower-stage recovery conveyor41 and a separation and take-out conveyor 42 both arranged below thelower-stage separating electrostatic field Ea2, the lower-stage recoveryconveyor 41 collecting the plastic pieces b electrified to the (−)polarity and attracted to the second drum electrode 11 or followingfalling trajectories approaching the upper-stage drum electrode 11, anda separation and take-out conveyor 42 that collects, with a high purity,a large number of plastic pieces a electrified to the (+) polarity andfalling from the lower-stage drum electrode 31 toward the lower-stageopposing electrode 32 owing to electrostatic force and centrifugalforce. Further, a second separator 43 is arranged between thelower-stage recovery conveyor 41 and the separation and take-outconveyor 42 to adjust the separation conditions for plastic pieces bseparated toward the lower-stage recovery conveyor 41, located closer tothe lower-stage drum electrode 31, and plastic pieces a and b separatedtoward the separation take-out conveyor 42, located closer to thelower-stage opposing electrode 32. The second separator 43 has aseparation plate arranged immediately below a peripheral side end of thelower-stage drum electrode 31 and the lower end of which is supported soas to be pivotable around an axis parallel with the axis of thelower-stage drum electrode 31. The separation plate is caused to pivotin the direction of an arrow in the figure by a manualrotationally-movable mechanism or actuator (not shown) so as to separatethe plastic pieces a and b from each other with a desired purity.

The upper-stage drum electrode 11 and the lower-stage drum electrode 31are set to, for example, have the same width, outside diameter, androtation speed so as to have an equal attraction area per unit time andthus equal processing capability in the upper-stage electrostaticseparating section 10 and the lower-stage electrostatic separatingsection 30.

With the above described construction, if the plastic pieces a and b arePE and PVC, respectively, and are contacted with each other by thetribo-electrifying device 1, then the plastic pieces a aretribo-electrified to the (+) polarity with a predeterminedelectrification amount while the PVC plastic pieces b aretribo-electrified to the (−) polarity with a predeterminedelectrification amount. Then, when these plastic pieces a and b aredropped from the supply chute 12 and fed onto the upper-stage drumelectrode 11 of the upper-stage electrostatic separating section-10, towhich the (−) polarity has been applied, then the plastic pieces a and bare attracted, by image force, to a surface of the upper-stage drumelectrode 11 and moved to the upper-stage sorting electrostatic fieldEa1. In the upper-stage sorting electrostatic field Ea1, the plasticpieces a and b are subjected to electrostatic force and centrifugalforce, and the plastic pieces a (PE), which are electrified to (+),remain attracted to the upper-stage drum electrode 11 or are separatedand dropped onto the upper-stage loading chute 21 by following tracksapproaching the upper-stage drum electrode 11. Furthermore, the plasticpieces b (PVC) electrified to (−) are repelled by the upper-stage drumelectrode 11, fall following tracks approaching the upper-stage opposingelectrode 13 and are then separated and collected by the intermediaterecovery conveyor 22. The plastic pieces b (including a small number ofplastic pieces a), which are collected by the intermediate recoveryconveyor 22, are returned to the tribo-electrifying device 1 by acirculating device (not shown).

Then, the plastic pieces a and b (including a small amount of plasticpieces b) collected in the upper-stage loading chute 21 are further fedonto the lower-stage drum electrode 31 of the lower-stage electrostaticseparating section 30, to which the (+) polarity has been applied. Then,the plastic pieces a and b are attracted, by image force, to a surfaceof the lower-stage drum electrode 31 and moved to the lower-stageseparating electrostatic field Ea2. In the lower-stage Separatingelectrostatic field Ea2, a small number of plastic pieces b electrifiedto (−) remain attracted to the lower-stage drum electrode 31, having the(+) polarity, or-most of them fall following tracks approaching thelower-stage drum electrode 31 and are collected on the lower-stagerecovery conveyor 41. On the other hand, a large amount of plasticpieces a electrified to (+) are subjected to electrostatic force andcentrifugal force and are repelled by the lower-stage drum electrode 31.The large amount of plastic pieces a fall following tracks approachingthe lower-stage opposing electrode 32 and are collected on theseparation and take-out conveyor 42 with a high purity and a highrecovery rate. In this embodiment, the two types of plastic pieces aresorted out, but a plurality of types may be used. Further, if theplastic pieces b separated and collected on the lower-stage recoveryconveyor 41 solely have a high purity, they may be used as sortedplastic pieces as they are. On the contrary, if they have a low purityor plural types of plastic pieces are mixed together, the lower-stagecirculating device (not shown) returns the plastic pieces to thetribo-electrifying device 1.

The inventors have experimentally confirmed that with the plasticsorting apparatus shown in FIG. 9 and comprising an endless belt-likeelectrode, described later, as well as a drum electrode and an opposingelectrode, the relationship between the mixture ratio of different typesof loaded plastic pieces and the purity of plastic pieces separatedtoward the opposing electrode is as shown in the graph of FIG. 2. Thisfigure indicates that the purity of plastic pieces of the type sortedout, separated and carried toward the opposing electrode increaseslinearly with the mixture ratio of these plastic pieces to the totalamount of plastic pieces loaded into the plastic sorting apparatus.

That is, with the above described plastic sorting apparatus, all plasticpieces are loaded onto the drum electrode, and the plastic pieces of thetype electrified to the polarity opposite to that of the drum electrodeare attracted to the surface thereof because of image force. Then, theseplastic pieces are rotationally moved downward to enter the separatingelectrostatic field, where these plastic pieces on the drum electrodeare subjected to centrifugal force and electrostatic force. At thistime, with few plastic pieces of the polarity opposite to that of thedrum electrode, it is very unlikely that the plastic pieces aresuperposed on one another or interfere with each other, and image forceand electrostatic force work effectively. Consequently, most of theplastic pieces of the opposite polarity can be reliably separated towardthe drum electrode, thereby enabling the recovery of these plasticpieces with a high purity and a high recovery rate.

Accordingly, if target plastics are to be separated from the otherplastic pieces with a high purity and a high recovery rate, this objectcan be attained by setting the electrification polarity of the separatedplastic pieces to be the same as that of the high voltage applied to thedrum electrode and further setting the amount of a different type ofplastic pieces provided to be smaller than that of the target type ofplastic-pieces to set a lower mixture ratio for the former type.

According to the above described embodiment, most of the plastic piecesa and b fed to the lower-stage electrostatic separating section 30 fromthe intermediate loading chute 21 of the upper-stage connection section20 are the plastic pieces a, which are electrified to the (+) polarity,because the amount of the plastic pieces b, electrified to the (−)polarity and separated by the upper-stage electrostatic separatingsection 10, is substantially reduced. Then, a high voltage of the (+)polarity is applied to the lower stage drum electrode 31 of thelower-stage electrostatic separating section 30 to reliably remove thesmall amount of plastic pieces b, thereby allowing the plastic pieces ato be collected on the separation and take-out conveyor 42 with a highpurity and a high recovery rate.

According to the inventors' experiments, when plastic pieces PE, whichare electrified to (+), and plastic pieces PVC, which are electrified to(−), were supplied to the tribo-electrifying device 1 after being mixedtogether so that the mixture ratio of 50% of the former to the latterwas 1:1, the plastic pieces PE could be collected on the separation andtake-out conveyor 42 of the recovery section 40 with a high purityexceeding 99% and a high recovery rate of 90% or more. In theexperiments, the amount of plastic pieces processed was 300 Kg/H, thedrum electrodes 11 and 31 had a peripheral velocity of about 50 m/sec,and a voltage of 30 KV was applied by the high-voltage power supply 2.

Next, a second embodiment of a plastic sorting apparatus will bedescribed with reference to FIG. 3. The same members as those in thefirst embodiment are denoted by the same reference numerals, and theirdescription is thus omitted.

In the second embodiment, the lower-stage electrostatic separatingsection 30 according to the first embodiment is provided with alower-stage upper-level electrostatic sorting section 50 and alower-stage lower-level electrostatic sorting section 70 which arearranged in the vertical direction, and connected together by alower-stage connection section 60.

That is, the lower-stage upper-level electrostatic sorting section 50comprises a lower-stage upper-level drum electrode 51 (rotationallymovable electrode) arranged below an exit of the upper-stage loadingchute 21 and rotationally driven in the direction of an arrow in thefigure (counterclockwise), a lower-stage upper-level opposing electrode52 arranged so as to form a space of a predetermined size between thelower-stage upper-level drum electrode 31 and the opposing electrode 52,and a lower-stage upper-level scraper 53 slidably contacting with thelower-stage upper-level drum electrode 51 to scrape off the plasticpieces therefrom. The positive electrode (+) of the high-voltage powersupply 2 is connected to the lower-stage upper-level drum electrode 51,while the negative electrode (−) thereof is connected to the lower-stageupper-level opposing electrode 0.52 via an earth. Consequently, alower-stage upper-level separating electrostatic field Ea3 is formedbetween the lower-stage upper-level drum electrode 51 and thelower-stage upper-level opposing electrode 52.

Furthermore, the lower-stage connection section 60 has a lower-stageloading chute 61 and a lower-stage recovery conveyor 62 both arrangedbelow the lower-stage upper-level separating electrostatic field Ea3,the lower-stage loading chute 61 collecting plastic pieces a (includinga small number of plastic pieces b) electrified to the (+) polarity andseparated toward the lower-stage upper-level opposing electrode 52, thelower-stage recovery conveyor 62 collecting plastic pieces b (includinga small number of plastic pieces a) electrified to the (−) polarity andseparated toward the lower-stage upper-level drum electrode 51. Further,a lower-stage separator (separator) is arranged below the lower-stageupper-level separating electrostatic field Ea3 and between thelower-stage loading chute 61 and the lower-stage recovery conveyor 62,and comprises a separation plate to adjust the separation conditions forplastic pieces a separated toward the lower-stage upper-level loadingchute 61 and plastic pieces b separated toward the lower-stage recoveryconveyor 62.

The lower-stage lower-level electrostatic sorting section 70 comprises alower-stage lower-level drum electrode 71 (rotationally-movableelectrode) arranged below an exit of the lower-stage loading guide chute61 and rotationally driven in the direction of an arrow in the figure(clockwise), a lower-stage lower-level opposing electrode 72 arranged soas to form a space of a predetermined size between the lower-level drumelectrode 71 and the opposing electrode 72, and a lower-stagelower-level scraper 73 slidably contacting with the lower-stagelower-level drum electrode 71 to scrape off the plastic piecestherefrom. The positive electrode (+) of the high-voltage power supply 2is connected to the lower-stage lower-level drum electrode 71, while thenegative electrode (−) thereof is connected to the lower-stagelower-level opposing electrode 72 via an earth. Consequently, alower-stage lower-level separating electrostatic field Ea4 is formedbetween the lower-stage lower-level drum electrode 71 and thelower-stage lower-level opposing electrode 72.

According to the above described second embodiment, plastic pieces a andb separated toward the lower-stage upper-level opposing electrode 52 inthe lower-stage upper-level electrostatic sorting section 50 are fed tothe lower-stage lower-level electrostatic separating section 70 via thelower-stage loading chute 61 of the lower-stage connection section 60.At this time, most of the plastic pieces a and b are plastic pieces aseparated by the lower-stage upper-level electrostatic separatingsection 50 of the upper-stage electrostatic separating section 10 andmost of which have been electrified to (+). These plastic pieces a aremixed with plastic pieces b slightly electrified to (−). When theplastic pieces a and b are fed to the lower-level lower-stageelectrostatic sorting section 70, a large amount of plastic pieces a areseparated and collected on the separation and take-out conveyor 42 witha high purity and a high recovery rate, the conveyor 42 being locatedcloser to the lower-stage lower-level opposing electrode 72. Inaddition, a small number of plastic pieces b are reliably separated andcollected on the lower-stage recovery conveyor 41, located closer to thelower-stage lower-level drum electrode 71.

Consequently, the different types of plastic pieces can be separatedfrom each other with a higher purity and a higher recovery rate than inthe first embodiment. Furthermore, even if the different types ofplastic pieces have only a small difference in electrification amounttherebetween, these types can be separated from each other with a highpurity and a high recovery rate.

Moreover, a third embodiment of a plastic sorting apparatus will bedescribed with reference to FIG. 4. The same members as those in theabove embodiments are denoted by the same reference numerals, and theirdescription is thus omitted.

In the first embodiment, plastic pieces a (including a small amount ofplastic pieces b) separated toward the upper-stage drum electrode 11 inthe upper-stage electrostatic separating section 10 are fed to thelower-stage electrostatic separating section 30 via the upper-stageconnection section 20. In this third embodiment, however, plastic piecesb (including a small amount of plastic pieces a) separated toward theupper-stage opposing electrode 13 in the upper-stage electrostaticseparating section 10 are fed to the lower-stage electrostaticseparating section 90 via the upper-stage connection section 80.

The upper stage connection section 80 comprises an upper-stage loadingchute 81 that receives and feeds plastic pieces a and b separated towardthe upper-stage opposing electrode 13, to the lower-stage electrostaticseparating section 90, an upper-stage recovery conveyor 82 that receivesplastic pieces a and b separated toward the upper-stage drum electrode11, and an upper-stage separator 83 that can use a separation plate toadjust the separation conditions for the plastic pieces. The plasticpieces a and b collected on the upper-stage recovery conveyor 82 arereturned to the tribo-electrifying device 1 by the circulating device(not shown) as required.

Further, the lower-stage electrostatic separating section 90 comprises alower-stage drum electrode 91, a lower-stage opposing electrode 92, anda lower-stage scraper 93 as in the case with the first embodiment, butdiffers therefrom in that the positive electrode (+) of the high-voltagepower supply 2 is connected to the lower-stage opposing electrode 92,while the negative electrode (−) thereof is connected to the lower-stagedrum electrode 91 via an earth. A lower-stage separating electrostaticfield Ea5 is formed between the lower-stage drum electrode 91 and thelower-stage opposing electrode 92.

According to the above described third embodiment, plastic pieces b(including a small amount of plastic pieces a) separated toward theupper-stage opposing electrode 13 in the upper-stage electrostaticseparating section 10 are fed to the lower-stage drum electrode 91 ofthe lower-stage electrostatic separating section 90 via the upper-stageloading chute 81 of the upper-stage connection section 80. A largeamount of plastic pieces b, which have been electrified to (−), areseparated toward the lower-stage opposing electrode 92 and received bythe separation and take-out conveyor 42, whereas a small amount ofplastic pieces at which have been electrified to (+), are separatedtoward the lower-stage drum electrode 91 and received by the lower-stagerecovery conveyor 41. Accordingly, a large amount of plastic pieces bcan be separated from the plastic pieces a with a high purity and a highrecovery rate. Further, the graph of FIG. 2 indicates that if of theplastic pieces a and b loaded from the tribo-electrifying device 1, thetarget plastic pieces b have a higher mixture ratio than the plasticpieces a, then the plastic pieces b can be separated and collected onthe separation and take-out conveyor 42 with a higher purity and ahigher recovery rate.

Furthermore, a fourth embodiment of a plastic sorting apparatus will bedescribed with reference to FIG. 5. The same members as those in theabove embodiments are denoted by the same reference numerals, and theirdescription is thus omitted.

In this fourth embodiment, the lower-stage electrostatic sorting section90 of the third embodiment is constructed similarly to the secondembodiment, and high voltages of the same polarities as those in theupper-stage electrostatic sorting section 10 are applied to thelower-stage upper-level electrostatic sorting section 60 and lower-stagelower-level electrostatic sorting section 70 by the high-voltage powersupply 2.

According to the fourth embodiment, as in the second embodiment, plasticpieces b separated toward the upper-stage opposing electrode 13 in theupper-stage electrostatic separating section 10 can further be separatedand collected on the separation and take-out conveyor 42 with a highpurity and a high recovery rate. Even if the different types of plasticpieces have only a small difference in electrification amounttherebetween, these types can be separated from each other with a highpurity and a high recovery rate. Further, the graph of FIG. 2 indicatesthat if of the plastic pieces loaded from the tribo-electrifying device71, the target plastic pieces b have a higher mixture ratio than theplastic pieces a, then the plastic pieces b can be separated from theplastic pieces a with a higher purity and a higher recovery rate.

Furthermore, FIG. 6 shows a fifth embodiment of a plastic sortingapparatus.

This plastic sorting apparatus is obtained by merging the first andthird embodiments together, and comprises the single upper-stageelectrostatic separating section 10 used for the purposes of bothembodiments, and a lower-stage first and second electrostatic sortingsections 30A and 30B and a first and second recovery sections 40A and40B all of which are arranged below the upper-stage electrostaticsorting section 10 via an upper-stage connection section 25.

That is, the upper-stage connection section 25 is provided with anupper-stage first loading chute 26 that receives and feeds plasticpieces a (including a small amount of plastic pieces b) separated towardthe upper-stage drum electrode 11, to the lower-stage firstelectrostatic sorting section 30A, an upper-stage second loading chute27 that receives and feeds plastic pieces b (including a small amount ofplastic pieces a) separated toward the upper-stage opposing electrode13, to the lower-stage second electrostatic sorting section 30B, and anupper-stage separator 28.

Further, the lower-stage first electrostatic sorting section 30Acomprises a lower-stage first drum electrode (rotationally movableelectrode) 31A arranged below an exit of an upper-stage first loadingchute 21A and rotationally driven in the direction of an arrow in thefigure (counterclockwise), a lower-stage first opposing electrode 32Aarranged so as to form a space of a predetermined size between thelower-stage first drum electrode 31A and the opposing electrode 32A, anda lower-stage first scraper 33A that scrapes off the plastic pieces bfrom the lower-stage first drum electrode 31A. The positive electrode(+) of the high-voltage power supply 2 is connected to the lower-stagefirst drum electrode 31A, while the negative electrode (−) thereof isconnected to the lower-stage first opposing electrode 32A via an earth.Consequently, a lower-stage first separating electrostatic field Ea6 isformed between the lower-stage first drum electrode 31A and thelower-stage first opposing electrode 32A.

The first recovery section (recovery section) 40A has a lower-stagefirst recovery conveyor 41A and a lower-stage first separation andtake-out conveyor 42A, the lower-stage first recovery conveyor 41Areceiving plastic pieces b separated toward the lower-stage first drumelectrode 31A, the lower-stage first separation and take-out conveyor42A receiving plastic pieces a separated toward the lower-stage firstopposing electrode 32A. The plastic pieces b on the lower-stage firstrecovery conveyor 41A are returned to the tribo-electrifying device 1 bythe circulating device (not shown) as required.

Further, the lower-stage second electrostatic sorting section 30Bcomprises a lower-stage second drum electrode (rotationally movableelectrode) 31B arranged below an exit of the second loading chute 21Band rotationally driven in the direction of an arrow in the figure(counterclockwise), a lower-stage second opposing electrode 32B arrangedso as to form a space of a predetermined size between the lower-stagesecond drum electrode 31B and the opposing electrode 32B, and alower-stage second scraper 33B slidably contacting with the lower-stagesecond drum electrode 31B to scrape off the attracted plastic pieces atherefrom. The positive electrode (+) of the high-voltage power supply 2is connected to the lower-stage second opposing electrode 32B, while thenegative electrode (−) thereof is connected to the lower-stage seconddrum electrode 31B via an earth. Consequently, a lower-stage secondseparating electrostatic field Ea7 is formed between the lower-stagesecond drum electrode 31B and the lower-stage second opposing electrode32B.

The second recovery section (recovery section) 40B has a lower-stagesecond recovery conveyor 41B and a lower-stage second separation andtake-out conveyor 42B, the lower stage second recovery conveyor 41Breceiving plastic pieces a separated toward the lower-stage second drumelectrode 31B, the lower-stage second separation and take-out conveyor42B receiving plastic pieces b separated toward the lower-stage secondopposing electrode 32B. The plastic pieces a on the lower-stage secondrecovery conveyor 41B are returned to the tribo-electrifying device 1 bythe circulating device (not shown) as required.

According to the above described embodiment, the plastic pieces a and bseparated by the upper-stage electrostatic separating section 10 are fedto the lower-stage first electrostatic sorting section 30A and to thelower-stage second electrostatic sorting section 30B for separation. Ofthe plastic pieces a and b supplied by the upper-stage first loadingchute 21A, a small amount of plastic pieces b are separated toward thelower-stage first drum electrode 31A in the lower-stage firstelectrostatic sorting section 30A, while a large amount of plasticpieces a are separated toward the lower-stage first opposing electrode32B. Consequently, the plastic pieces a to be collected on thelower-stage first separation and take-out conveyor 42A can be separatedfrom the other plastic pieces with a high purity and a high recoveryrate. Further, of the plastic pieces a and b supplied by the upper-stagesecond loading chute 21B, a small amount of plastic pieces a areseparated toward the lower-stage second drum electrode 31B in thelower-stage second electrostatic sorting section 30B, while a largeamount of plastic pieces b are separated toward the lower-stage secondopposing electrode 32B. Consequently, the plastic pieces b to becollected on the lower-stage second separation and take-out conveyor 42Bcan be separated from the other plastic pieces with a high purity and ahigh recovery rate. Therefore, if two or plural types of plastic piecesare to be separated from each other, plastic pieces a having the largestelectrification amount on the (+) side and plastic pieces b having thelargest electrification amount on the (−) side can be simultaneouslyseparated from the other plastic pieces with a high purity and a highrecovery-rate.

Further, FIG. 7 shows a sixth embodiment of a plastic sorting apparatus.

This plastic sorting apparatus is obtained by merging the second andfourth embodiments together, wherein the lower-stage first electrostaticseparating section 30A is composed of a lower-stage first upper-levelelectrostatic sorting section 50A, a lower-stage first connectionsection 60A, and a lower-stage first lower-level electrostatic sortingsection 70A, and the lower-stage second electrostatic sorting section30B is composed of a lower-stage second upper-level electrostaticsorting section 50B, a lower-stage second connection section 60B, and alower-stage second lower-level electrostatic sorting section 70B.

That is, the lower-stage first upper-level electrostatic sorting section50A comprises a lower-stage first upper-level drum electrode 51A(rotationally movable electrode) arranged below an exit of theupper-stage first loading chute 21A, a lower-stage first upper-levelopposing electrode 52A, and a lower-stage first upper-level scraper 53A.The positive electrode (+) of the high-voltage power supply 2 isconnected to the lower-stage first upper-level drum electrode 51A, whilethe negative electrode (−) thereof is connected to the lower-stage firstupper-level opposing electrode 52A via an earth. Consequently, alower-stage first upper-level sorting electrostatic field Ea8 is formedbetween the lower-stage first upper-level drum electrode 51A and thelower-stage first upper-level opposing electrode 52A.

Further, the lower-stage first connection section 60A has a lower-stagefirst loading chute 61A and a lower stage first recovery conveyor 62Aboth arranged below the lower-stage first upper-level sortingelectrostatic field Ea8, the lower-stage first loading chute 61Acollecting plastic pieces a (including a small number of plastic piecesb) separated toward the lower-stage upper-level drum electrode 11, thelower-stage first recovery conveyor 62A collecting plastic pieces b(including a small number of plastic pieces a) separated toward theupper-stage opposing electrode 13. Further, a lower-stage firstseparator (separator) 63A is provided which causes a separation plate topivot so as to adjust the separation conditions for plastic pieces bseparated toward the lower-stage first upper-level drum electrode 51Aand plastic pieces a separated toward the lower-stage first upper-levelopposing electrode 52A.

Further, the lower-stage first lower-level electrostatic sorting section70A comprises a lower-stage first lower-level drum electrode(rotationally movable electrode) 71A arranged below an exit of thelower-stage first loading guide chute 61A, a lower-stage firstlower-level opposing electrode 72A, and a lower-stage first lower-levelscraper 73A. The positive electrode (+) of the high-voltage power supply2 is connected to the lower-stage first lower-level drum electrode 71A,while the negative electrode (−) thereof is connected to the lower-stagefirst lower-level opposing electrode 72A via an earth. Consequently, alower-stage first lower-level sorting electrostatic field Ea9 is formedbetween the lower-stage first lower-level drum electrode 71A and thelower-stage first lower-level opposing electrode 72A.

The first recovery section 40A, located below the lower-stage firstlower-level sorting electrostatic field Ea9, is provided with alower-stage first recovery conveyor 41A that receives plastic pieces bseparated toward the lower-stage first lower-level drum electrode 71A, afirst separation and take-out conveyor 42A that receives plastic piecesa separated toward the lower-stage first lower-level opposing electrode72A, and a lower-stage first separator 43A that can adjust the abovedescribed separation conditions.

Furthermore, the lower-stage second upper-level electrostatic sortingsection SOB comprises a lower-stage second upper-level drum electrode51B (rotationally movable electrode) arranged below an exit of thesecond upper-stage loading chute 21B, a lower-stage second upper-levelopposing electrode 52B, and a lower-stage second upper-level scraper53B. The positive electrode (+) of the high-voltage power supply 2 isconnected to the lower-stage second upper-level opposing electrode 52B,while the negative electrode (−) thereof is connected to the lower-stagesecond upper-level drum electrode 51B via an earth. Consequently, alower-stage upper-level separating electrostatic field Ea10 is formedbetween the lower-stage second upper-level drum electrode 51B and thelower-stage second upper-level opposing electrode 52B.

Further, the second lower-stage connection section 60B has a lower-stagesecond loading chute 61B and a lower-stage second recovery conveyor 62Dboth arranged therein, the lower-stage second loading chute 61Bcollecting plastic pieces a (including a small number of plastic piecesb) separated toward the lower-stage second upper-level drum electrode51B, the lower-stage second recovery conveyor 62B collecting plasticpieces b (including a small number of plastic pieces a) separated towardthe upper-stage second upper-level opposing-electrode 53B. Further, alower-stage second separator (separator) 63B is provided which causes aseparation plate to pivot so as to adjust the separation conditions forplastic pieces b separated toward the lower-stage second upper-leveldrum electrode 51B and plastic pieces b separated toward the lower-stagesecond-upper-level opposing electrode 52B.

Furthermore, the lower-stage second lower-level electrostatic sortingsection 70B comprises a lower-stage second lower-level drum electrode(rotationally movable electrode) 71B arranged below an exit of thelower-stage second loading guide chute 61B, a lower-stage secondlower-level opposing electrode 72B, and a lower-stage second lower-levelscraper 73B. The positive electrode (+) of the high-voltage power supply2 is connected to the lower-stage second lower-level opposing electrode72B, while the negative electrode (−) thereof is connected to thelower-stage second lower-level drum electrode 71B via an earth.Consequently, a lower-stage second lower-level sorting electrostaticfield. Ea11 is formed between the lower-stage second-lower-level drumelectrode 71B and the lower-stage second lower-level opposing electrode72B.

The second recovery section 40B, located below the lower-stage secondlower-level sorting electrostatic field Ea11, is provided with alower-stage second recovery conveyor 41B that receives plastic pieces aseparated toward the lower-stage second lower-level drum electrode 71B,a second separation and take-out conveyor 42B that receives plasticpieces a separated toward the lower-stage second lower-level opposingelectrode 72B, and a lower-stage second separator 43B that can adjustthe above described separation conditions.

According to the above described embodiment, the second and fourthembodiments are combined together, so that the plastic pieces a, whichare electrified to (+), and the plastic pieces b, which are electrifiedto (−), can be simultaneously collected on the first and secondseparation and take-out conveyors 42A and 42B, respectively, with ahigher purity and a higher recovery rate. Even if the different types ofplastic pieces have only a small difference in electrification amounttherebetween, these types can be separated from each other with a highpurity and a high recovery rate.

Moreover, in the first to sixth embodiments, the rotationally movableelectrode is a drum electrode but may be composed of a metallicbelt-like endless belt electrode 97 wound around and extended betweenrotating members 95 and 96 arranged horizontally opposite each other andparallel with each other as shown: in FIG. 8. In this case, by setting atravel path at the top of the belt electrode 97 to extend in thehorizontal direction and feeding plastic pieces onto this horizontalportion 97 a, the plastic pieces can be stably attracted to a surface ofthe belt electrode 97 using image force and can then be fed into aseparating electrostatic field Ea formed between the belt electrode 97and an opposing electrode 98 arranged obliquely above a portion of thebelt electrode 97 which rotationally moves downward. As a result, theseparation precision can further be improved.

Furthermore, in the second, fourth, and sixth embodiments, thelower-stage electrostatic sorting section comprises an upper- andlower-level electrostatic sorting sections. However, the apparatus mayhave three or more electrostatic sorting sections arranged therein.

INDUSTRIAL APPLICABILITY

As described above, the plastic sorting apparatus according to thepresent invention is suitable for separating plastic crushed pieces tobe collected and recycled, from one another according to their type witha high purity and a high recovery rate.

1. A plastic sorting apparatus, comprising: a tribo-electrifying sectionfor causing plural types of plastic pieces to frictionally contact withone another for electrification; and an upper-stage electrostaticseparating section, a lower-stage electrostatic separating section and arecovery section all of which are located below the tribo-electrifyingsection downwardly in this order, wherein the upper- and lower-stageelectrostatic separating sections each comprises a metallicrotationally-movable electrode having a top portion onto which plasticpieces are fed, an opposing electrode located to oppose a portion of therotationally movable electrode which moves rotationally downward, and ahigh-voltage power supply that applies a high voltage to saidrotationally movable electrode and opposing electrode to form aseparating electrostatic field therebetween, a connection section isprovided for feeding plastic pieces separated toward the rotationallymovable electrode in the upper-stage electrostatic separating section tothe rotationally movable electrode in the lower-stage electrostaticseparating section, and polarities applied by the high-voltage powersupply respectively to the rotationally movable electrode and theopposing electrode in the upper-stage electrostatic separating sectionare opposite to those in the lower-stage electrostatic separatingsection.
 2. The plastic sorting apparatus according to claim 1, whereinthe connection section includes a separator located therein foradjusting separation conditions of the plastic pieces separated towardthe rotationally movable electrode and the plastic pieces separatedtoward the opposing electrode.
 3. The plastic sorting apparatusaccording to claim 1, wherein the lower-stage electrostatic separatingsection is composed of a plurality of electrostatic separating sectionsarranged in a vertical direction and each comprising a rotationallymovable electrode, an opposing electrode and a high-voltage powersupply, and plastic pieces separated from another plastic pieces towardthe opposing electrode in the upper-level lower-stage electrostaticseparating section are fed to a lower-level rotationally-movableelectrode via the connection section, and wherein polarities of a highvoltage applied by the high-voltage power supply respectively to therotationally movable electrode and the opposing electrode in theuppermost lower-stage electrostatic separating section are the same asthose in the lower-stage electrostatic separating section located belowthe uppermost lower-stage electrostatic separating section.
 4. A plasticsorting apparatus, comprising: a tribo-electrifying section for causingplural types of plastic pieces to frictionally contact with one anotherfor electrification; and an upper-stage electrostatic separatingsection, a lower-stage electrostatic separating section and a recoverysection which are arranged below the tribo-electrifying sectiondownwardly in this order, wherein the lower-stage electrostaticseparating section includes therein a lower-stage first electrostaticseparating section to which plastic pieces separated toward therotationally movable electrode in the upper-stage electrostaticseparating section are fed via a connection guide section, and alower-stage second electrostatic separating section to which plasticpieces separated toward the opposing electrode in the upper-stageelectrostatic separating section are fed, the upper-stage electrostaticseparating section and the lower-stage first and second electrostaticseparating sections each comprises a metallic rotationally-movableelectrode having a top portion onto which plastic pieces are fed, anopposing electrode arranged to oppose a portion of the rotationallymovable electrode which rotationally moves downward, and a high-voltagepower supply that applies a high voltage to the rotationally movableelectrode and the opposing electrode to form a separating electrostaticfield therebetween, the polarity of a high voltage applied to theupper-stage electrostatic separating section by the high-voltage powersupply thereof is opposite to the polarity of a high voltage applied tothe lower-stage first electrostatic separating section by saidhigh-voltage power supply thereof, and the polarity of a high voltageapplied to the upper-stage electrostatic separating section by saidhigh-voltage power supply thereof is the same as the polarity of a highvoltage applied to the lower-stage second electrostatic separatingsection by said high-voltage power supply thereof.
 5. The plasticsorting apparatus according to claims 1 and 5, wherein the rotationallymovable electrode comprises a cylindrical drum electrode located to berotatable around a horizontal axis.
 6. The plastic sorting apparatusaccording to claim 4, wherein the lower-stage first and secondelectrostatic separating sections each comprises a plurality ofelectrostatic separating sections each including a rotationally movableelectrode, an opposing electrode and a high-voltage power supply, thelower-stage first and second electrostatic separating sections eachincludes a connection section for feeding plastic pieces separatedtoward the opposing electrode in the upper-level lower-stage firstelectrostatic separating section, to the lower-levelrotationally-movable electrode, the polarity of a high voltage appliedby the high-voltage power supply to the rotationally movable electrodeand opposing electrode in the uppermost lower-stage first electrostaticseparating section is the same as the polarity of a high voltage appliedby the high-voltage power supply to the rotationally movable electrodeand opposing electrode in the lower-stage first electrostatic separatingsection located below the uppermost lower-stage first electrostaticseparating section, and the polarity of a high voltage applied by thehigh-voltage power supply to the rotationally movable drum and opposingelectrode in the uppermost lower-stage second electrostatic separatingsection is the same as the polarity of a high voltage applied by thehigh-voltage power supply to the rotationally movable drum and opposingelectrode in the lower-stage second electrostatic separating sectionlocated below the uppermost lower-stage second electrostatic separatingsection.
 7. The plastic sorting apparatus according to claim 5 or 6,wherein the connection section includes a separator located therein foradjusting separation conditions of the plastic pieces separated towardthe rotationally movable electrode and the plastic pieces separatedtoward the opposing electrode.